This application relates generally to rotary machines and more particularly, to methods and apparatus for sealing a rotary machine.
At least some known rotary machines such as, but not limited to steam turbines and gas turbines, include a plurality of seal assemblies in a steam-flow path or a flow path to facilitate increasing operating efficiency of the rotary machine. At least some known seal assemblies are coupled between a stationary component and a rotary component to provide sealing between a high-pressure area and a low-pressure area. For example, to facilitate thrust balancing, a turbine rotor may be sealed relative to a cooperating stator to facilitate maintaining a higher pressure in a forward direction of the rotor as compared to a lower pressure in an aft direction of the rotor.
At least some known seal assemblies include seal members such as, but not limited to, brush seals and/or compliant plates. Compliant plates such as, but not limited to, leaf seals, shingles seals, and/or intermediate plate seals are generally aligned in a pack and oriented in a circumferential direction about a central rotational axis of a rotary component. More specifically, the compliant plates are generally arranged to engage and disengage the rotor or rotary component during various operating conditions of the rotary machine. For example, during shut down of the turbine engine, a portion of the compliant plates are generally in contact with a rotary component. During rotation of the rotary component, various forces generally act on the compliant plates to cause the plates to deflect upward. Such forces include, but are not limited to, compliant plate/rotor contact forces, hydrodynamic lifting forces, and differential pressure forces. Compliant plate/rotor contact forces are generated during contact between the compliant plate and the rotary component. Hydrodynamic lifting forces are generated by rotation of the rotary component. Differential pressure forces include radially outward lifting forces and radially inward blow-down forces that are generated due to the static pressure distribution on the compliant plates. Because a small amount of clearance between tips of the compliant plates and the rotary component facilitates reducing wearing of the compliant plates, a balance between such forces acting on the compliant plates is desirable to minimize seal leakage and to ensure that the compliant plate tips are disengaged from the rotary component during rotor rotation.
At least some known seal assemblies include a seal housing that includes at least a high-pressure-side front plate and a low-pressure-side back plate that is substantially parallel to, and spaced a fixed distance from, the front plate to define a cavity. In such seal assemblies, a physical gap between the compliant plates and the front plate, and a physical gap between the compliant plates and the back plate, are each defined based on the positional mounting of the compliant plates within the cavity. Known seal assemblies are generally assembled in an attempt to define some known specified gap widths between the seal housing and the compliant plates.
Generally, variations in sizes of the physical gaps are known to influence compliant plate movement and radial flow leakage in the seal assemblies. As such, known seal assemblies generally require smaller manufacturing tolerances to facilitate having actual widths of the gaps after manufacturing and assembly of the seals to be closer to the desired gap widths. However, fabricating seal assemblies with tighter tolerances to define smaller desirable gaps generally increases the fabrication complexity and the fabrication costs as compared to seal assemblies that are fabricated with larger tolerances to define larger gaps. Moreover, deviations from the specified gap sizes may cause the seal housing and the compliant plates of some known seal assemblies to rub and create frictional forces. Rubbing and/or frictional forces may reduce seal assembly life and/or increase the overall maintenance cost of the machine.